1. Field of the Invention
The invention relates to a method for the production of a superconducting electrical conductor which has a ceramic material as the superconducting material, and to a superconducting conductor.
2. Description of Related Art
A superconducting electrical conductor which can be produced using the method according to the invention is composed of a composite material whose superconducting ceramic material changes to the superconducting state at sufficiently low temperatures. The electrical direct-current resistance of a conductor formed from a material such as this is zero when adequate cooling is provided, provided that a specific current level is not exceeded. Suitable ceramic materials are, for example, BSCCO (bismuth-strontium-calcium-copper oxide) or ReBCO (rare-earth barium-copper oxide), in particular YBCO (yttrium-barium-copper oxide). By way of example, sufficiently low temperatures to change a material such as this to the superconducting state are between 67 K and 110 K. Suitable coolants are, for example, nitrogen, helium, neon and hydrogen, or mixtures of these substances.
U.S. Pat. No. 5,739,086 describes various methods for production of electrical conductors which are in the form of ribbons and are referred to as high-temperature superconductors. In the case of a BSCCO superconductor, the BSCCO material is, for example, introduced in powder form into a tube composed of silver, and is compressed. The superconducting state is achieved by mechanical deformation of the tube and subsequent heat treatment (annealing). Tn the case of a YRCO superconductor, which is particularly suitable for electrical cables and windings because of its excellent electrical characteristics, a buffer layer that is likewise composed of metal, is first of all applied to a ribbon, which for example is biaxially textured and composed of metal as a substrate, onto which buffer layer the YBCO material is the applied. The substrate is composed, for example, of nickel, copper or iron, or of an alloy of these materials. By way of example, copper or silver is used for the buffer layer. Finally, the YBCO material is likewise changed to the superconducting state by heat treatment. The superconducting conductor that is being produced in this way can—as already mentioned—advantageously be used in electrical cables as well as windings for electric motors and magnets. In this case, however, it can be bent in only one direction, because it is in the form of a ribbon.
The method according to the initially cited EP 1 916 720 B1 results in a round superconducting conductor being produced, which can be processed in the same way as a conventional wire without having to maintain a particular direction during bending. This known method is used to form a textured metallic substrate, which is in the form of a ribbon, first of all in its longitudinal direction about an elongated, metallic mount with a circular cross section, to form a slotted tube with edges which extend in the longitudinal direction and rest on one another on a slot. The slotted tube is then closed by welding the slot. The closed tube is then pulled down until it makes contact with the mount. The superconducting ceramic material is then applied to the tube all round, and the heat treatment process is finally carried out. This method has been proven in practice. However, it involves a relatively large amount of effort. The superconducting material located on the outside can furthermore easily be damaged unless additional measures are taken.